1. Field of the Invention
The present invention relates to a radial tire for an airplane which is used in airplanes such as passenger jet planes or the like, and to a method of manufacturing the radial tire for an airplane.
2. Description of the Related Art
Conventionally, structures such as disclosed in WO 2003/061991 have been known as a radial tire for an airplane. As shown in FIG. 7, the radial tire for an airplane disclosed in WO 2003/061991 has an endless zigzag belt ply in which cords, which extend in the circumferential direction while zigzagging by being folded over at both ends of the ply, are embedded substantially uniformly at the entire region.
In a radial tire having such an endless zigzag belt ply, the cut ends of the cords are not exposed at the both ends of the belt. Therefore, even in cases in which the angle of inclination of the cords with respect to the tire equatorial plane is made to be small in an attempt to improve the total strength of the belt, the shearing strain between layers at the ends of the belt is low, and it is difficult for belt end separation to arise. As a result, the belt layer can be made to be lighter-weight by reducing the total number of belt plies while maintaining the prescribed safety rate. Further, this lightening of the weight of the belt layer can suppress the occurrence of a standing wave during high-speed traveling such as immediately before takeoff on a runway. Therefore, tires having the above-described endless zigzag belt ply are extremely well suited to be tires for airplanes.
In the endless zigzag belt ply having the above-described structure, in cases such as when a belt width W changes among plural layers or the like, the need arises to make the angle of bending of the cords at the ply end be different from those of the adjacent cords. Accordingly, as shown in FIG. 7, when the belt width changes from W1 to W2, the angle of intersecting a tire equatorial plane E also varies from θ1 to θ2. Between adjacent cords before and behind the change, a gap H arises, overlapping I arises, the rubber between the cords within the belt after vulcanization cannot be sufficiently ensured, and strain increases.
Further, in a tire in which the above-described endless zigzag belt ply and a spiral belt ply, in which inextensible, high elastic modulus cords are wound spirally in the tire circumferential direction, are layered, there is little change in the cord angles of the endless zigzag belt ply within the mold at the time of vulcanization. Therefore, after vulcanization as well, the aforementioned gap H and overlapping I remain, and this is a cause of an increase in strain. Such strain is an impediment to improving the durability of the pneumatic radial tire for an airplane.